The present disclosure relates to a monolithic spectrometer and an optical instrument comprising the monolithic spectrometer.
A spectrometer is an instrument used to probe a property of light as a function of its portion of the electromagnetic spectrum, e.g. for spectrally resolving the light. The term ‘light’ as used herein includes all forms of electromagnetic radiation such as visible, infrared and/or ultraviolet radiation. Typically, a spectrometer comprises reflective and/or refractive optics for guiding and shaping the light as well as a spectral resolving element such as a grating or prism for diffracting and/or dispersing the light in a wavelength dependent angle. Depending on the angle, different spectral components of the light can be imaged at different locations along a spectral axis in an imaging plane of the spectrometer. A sensor can be arranged for detecting spectral components of the light in the imaging plane.
A monolithic spectrometer comprises a body of solid material shaped to guide the light along an optical path inside the body. The body material is transparent at least to the wavelengths of light for which the spectrometer is intended to be used. For example, depending on the intended use, the material can be transparent to visible and/or infrared and/or ultraviolet radiation. The body shape comprises optical surfaces to transmit, reflect, shape (e.g. collimate or focus), refract (e.g. bend or disperse), and/or diffract the light as it travels along the optical path. Optionally, the optical surfaces may be coated, e.g. with a reflective material, or an optical piece such as a mirror or grating can be adhered to the optical surface to provide or aid the optical function of the surface. Advantages of a monolithic spectrometer over a regular spectrometer may include compactness, stability, and/or manufacturability.
One design of a monolithic spectrometer comprises an entry surface, a collimating surface, a grating surface, a focusing surface, and an exit surface. The entry surface is arranged to receive the light to enter into the body directed along a first part of the optical path. The collimating surface is arranged to receive the entering light directed along the first part of the optical path and to reflect said entering light as a collimated beam directed along a second part of the optical path. The grating surface is arranged to receive the collimated beam directed along the second part of the optical path and to reflect a diffracted beam directed along a third part of the optical path according to a wavelength dependent diffraction angle. The focusing surface is arranged to receive the diffracted beam directed along the third part of the optical path and to focus said diffracted beam directed along a fourth part of the optical path for imaging a wavelength component of the light onto a position along a spectral axis in an imaging plane outside the body. The exit surface is arranged in the optical path between the focusing surface and the imaging plane to have the light exit the body.
For example, U.S. Pat. No. 8,345,226 describes various embodiments of monolithic spectrometers including Czerny-Turner, crossed Czerny-Turner, and Fastie-Ebert configurations.
There is yet a need for an improved monolithic spectrometer that is both compact and easy to manufacture.